Electronic apparatus

ABSTRACT

A power supply for small integrated circuit devices which utilize a nominal supply voltage of 1.5 V but which are energized by a long-life lithium-iodine battery having a terminal voltage of 2.8 V. The power supply reduces the voltage to the integrated circuit to the required 1.5 V and also provides a means for delivering current peaks to a device operated by the integrated circuit, such as a stepping motor or LED display, while maintaining a relatively constant supply voltage to the integrated circuit.

The present invention relates to an electronic apparatus, and morespecifically a small portable apparatus having a long life solid statebattery, more particularly still to a lithium-iodine battery, anintegrated circuit and either a liquid crystal display, a light emittingdiode display or a motor driven analog display. An advantage of suchapparatus is that they work for example up to 10 years without changingthe battery. However, in order to attain even small dimensions the powersupply circuit must be optimalized. The internal resistance of thebatteries is relatively high so that they cannot directly delivercurrent peaks such as those which occur during switching processes andmore particularly during the driving pulses of a stepping motor orduring intermittent switching on of a light emitting diode, withoutrequiring a prohibitive increase of the active surface of the battery.

It is known that long life solid state batteries have a voltage of 2.8 Vand a characteristic of voltage which depends on the ratio of theinternal resistance to the load resistance. The internal resistance isvery high to prevent self discharge which is a decisive feature of thesebatteries. The most favourable practical resistance lies at about 50kOhm. With regard to this point, reference is made to the indications ofthe manufacturing company Catalyst Research Corp. and its U.S. Pat. Nos.3,660,163, 3,674,562 and 3,723,183.

It is well known that the kind of integrated circuit manufacturing whichis the most favorable of practical use in the above, the working voltageis about 1.5 V. The average operating current for the applicationsmentioned alone lies at about 2-5 μA so that with a capacity afterbattery of 300-400 mAh, a service life of more than 10 years may berealized. Although the functions of integrated circuits does not changeat higher voltages, one obtain a very high increase in current highervoltages, up to 50 uA which practically obviates the utilization of longlife batteries.

A lay out of an integrated circuit for an operating voltage of 2.8 Vwould lead to the further disadvantage that all production lines forcalculators or watches would have to be modified and further that thequality would decrease. Further a separate function would becomenecessary for those types of integrated circuits which presuppose arelatively small internal resistance power supply such as conventionalbatteries, as opposed to a lithium-iodine battery with solidelectrolyte. Because of the above indicated reasons, so called long lifebatteries are not capable of practical use in the above mentionedapplications. In order to avoid misunderstanding it is further mentionedthat lithium-iodine batteries with liquid electrolyte are alsoavailable. They have a unique capability to deliver very great amountsof energy for short periods of time. However like all batteries withliquid electrolyte, they share the disadvantage of a short service life.

The object of the present invention is to facilitate a breakthrough inthe utilization of long life solid state batteries such as for examplelithium-iodine batteries, for electronic small apparatus likecalculators or watches.

The electronic apparatus according to the present invention ischaracterized in that power is supplied at least for integrated circuitsthrough a resistor having a voltage drop of at least about 1.3 V and inthat a capacitor, having a capacity of 5 to 10 μF, is provided fordelivering peaks of current. This provides an adaptation of the voltageof the battery to the voltage of the integrated circuit and the peaks ofcurrent are delivered by the capacitor in such a way that no breakdownof the voltage at the integrated circuit and no disturbing of thefunction of the latter will occur. It is known that the internalresistance increases in accordance with the discharge time of thebattery. Nevertheless, in order to provide a constant operating voltage,at least for integrated circuits it is preferable to choose a resistancehaving a value many times greater than the internal resistance of thebattery. Particularly under such circumstances, it is important to holdthe current through the resistance at a relatively constant averagevalue in order to avoid excessive variations in the load voltage, forexample, the voltage across an integrated circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

An example of an embodiment of an electronic apparatus according to thepresent invention will be described further with the help of theaccompanying drawing.

FIG. 1 shows a schematic top view of a module of the apparatus with anexecution's variant,

FIG. 2 shows a schematic section of the module, and

FIG. 3 shows the diagram of connections.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The module represented in FIGS. 1 and 2 comprises a flat lithium-iodinebattery 1 above which is disposed a display unit 2 not represented inFIG. 1. The switching elements, more particularly an integrated circuit3, an oscillating quartz crystal 4, a capacitor 5, two resistances R1and R2, a change-over switch 6 with contacts 6a, 6b and 6c, a controlswitch 7 with contacts 7a to 7d and a light emitting diode 8 aredisposed between the battery 1 and display unit 2. The elements areconnected together as indicated in FIG. 1, contacts 9 and 10 beingconnected with the positive, and negative terminals of the battery 1. Ahold-fast 11 supports the switching elements and the module is heldtogether by means of a profile ring 12.

An embodiment variant is indicated by the broken lines in FIG. 1, andcomprises a stepping motor 13 having a corresponding integrated circuit14, instead of a liquid crystal display or the light emitting diodedisplay 2 in accordance with FIG. 2.

In the represented rest condition the integrated circuit is fed by thepositive terminal of the battery through the resistor R1 which producesa voltage drop of 1.3 V. At the same time the capacitor 5 is chargedthrough the closed contacts 6a and 6c. In order to activate the display,represented schematically by the diode 8 in FIG. 1, the contact 6a isturned over to contact 6b by a pusher (not illustrated whereby thedisplay 8 is energized by the capacitor long enough to permit reading ofit. The battery is therefore not loaded by the relatively high currentdemands of the display so that practically no variation in the voltageof the integrated circuit occurs which could produce a misfunction ofthe latter. The contacts 7a and/or 7c may be activated by a pusher (notillustrated) so that control pulses can be delivered over the contacts7b 7d respectively to control inputs of the integrated circuit 3.

Turning to the variant embodiment, the resistor R2, having a value ofbetween about 250 and 500 Ohms, is connected in the driving circuit ofthe stepping motor 13. In this embodiment driving pulses are deliveredfrom the capacitor 5 to the stepping motor 13 and experience has shownthat according to the type of the motor reliable operation is guaranteedby a capacitor of 5 to 10 μF. Such a capacitor occupies very littlespace and it can be practically in any small apparatus e.g. electronicwristwatches. The integrated circuit 14 is laid out for the full batteryvoltage of 2.8 V.

In the embodiment having light emitting diodes 8, the circuit can alsobe executed so that during the switching on of the display the effectiveresistance (R1) is decreased by providing a bridging resistor connectedin parallel with R1 by means of a switch operated together with thecontrol switch for the display. In this case the resistance R1 may havea value of e.g. 300 kOhm while the bridging resistance has a value of150 kOhm.

In FIG. 3, corresponding parts have the same references numerals as inFIG. 1 and only one integrated circuit 3 is shown which can drive eithera liquid crystal display (LCD), a light emitting diodes display 2 (LED)or a stepping motor 13 as represented schematically. In FIG. 3additional intermediate contacts 7e and 7f of the switch 7 which areconnected with the battery 1 through the resistor R2. As indicated by adashed line in FIG. 3, the resistor R2, in case of a light emittingdiodes display 2, is connected to the contacts 7e and 7f and it has e.g.the above mentioned value of 150 kOhm. A resistor R13 is connected inseries with the stepping motor 13 and has a value of e.g. about 250 to500 Ohm. As already mentioned, when one of the switches 7a or 7c isactivated, current is supplied to the integrated circuit 3 through theresistance R2 of decreased value for eliminating the influence of avoltage drop in the capacitor 5. In the case of the liquid crystaldisplay (LCD) and in the case of the stepping motor 13 which receivesvery short driving pulses such measures are not necessay.

The volume of the battery, of either form inclusive a protective capamounts to e.g. 1.2 cm³ for a capacity of 350 mAh. For a maximumconsumption of 4·10⁻⁶ A, one obtains a service life of about 10 years.

The diameter of the battery in FIGS. 1 and 2 amounts to e.g. 25 mm andthe height to 2.5 mm. A corresponding flat battery has e.g. a height of3 mm and a surface of 22×17 mm.

The module according to FIGS. 1 and 2 comprises e.g. a total height of6.7 mm and a diameter of 30 mm.

As already indicated, FIG. 3 is also a schematic representation.Normally the driving pulses for the stepping motor 13 are delivered bythe integrated circuit 3. Due to the fact that relative high peaks ofcurrent cannot occur through the relative high resistance R1, thecapacitor 5 is directly connected to the supply terminals of theintegrated circuit as indicated by the dashed line 15 in FIG. 3. In thiscase the resistance R1 is connected between the battery 1 and thecapacitor 5. In this case the contact 6c is no longer necessary and theresistors R2 or R13, whenever present, are directly connected to thecapacitor 5.

As indicated in FIG. 3, a change over switch 16 may be provided forseparating the load from the capacitor 5. The capacitor is thenconnected to a resistor 17 the value of which is selected so that thevoltage across the capacitor is held to the desired nominal voltagevalue of 1.5 V.

What I claim:
 1. An electronic apparatus energized by a long-life solidstate battery having a battery voltage comprising a first voltage level,said electronic apparatus comprising an integrated circuit operable tobe powered at a second voltage level lower than said first voltagelevel, and a load controlled by said integrated circuit, a power supplycircuit connected between the battery and the integrated circuitcomprising a resistance for dropping the first voltage level to thesecond voltage level, and a capacitor having a capacity of 5 to 10 μffor delivering peaks of current to the load.
 2. The apparatus accordingto claim 1, wherein said battery has an internal resistance and theresistance of the power supply circuit has a value which is a multipleof the internal resistance of the battery.
 3. The apparatus according toclaim 1 or 2, wherein the battery has an internal resistance of on theorder of 50 kOhm, the resistance of the power supply circuit has a valueof on the order of 300 kOhm.
 4. The apparatus according to claim 1 or 2wherein the capacitor is charged to the battery voltage and furthercomprising means, connected to the capacitor, for delivering saidcurrent peaks to the load.
 5. The apparatus according to claim 1 or 2further comprising a switch between the capacitor and load, said switchbeing operable for extracting current peaks from the capacitor.
 6. Theapparatus according to claim 1 or 2 further comprising a switch meansfor decreasing the value of the resistance of the power supply circuitduring the occurence of current peaks.
 7. The apparatus according toclaim 6, wherein said switch means comprises a control switch havingcontacts for the changing the resistance of the power supply circuit. 8.The apparatus according to claim 1, wherein the integrated circuit hassupply terminals and the capacitor is connected to the supply terminalsand the resistance is connected between the battery and the capacitor.9. The apparatus according to claim 4 further comprising a switchbetween the capacitor and load, said switch being operable forextracting current peaks from the capacitor.
 10. The apparatus accordingto claim 5 further comprising characterized a switch means fordecreasing the value of the resistance of the power supply circuitduring the occurrence of current peaks.
 11. The apparatus according toclaim 1 wherein the first voltage level is on the order of 2.8 V and thesecond voltage level is on the order of 1.5 V.
 12. An electronicapparatus adapted to be energized by a long-life lithium-iodine batteryhaving an internal resistance and a battery voltage level, saidapparatus including an integrated circuit operable to be powered at anoperating voltage level lower than battery voltage level, a loadcontrolled by said integrated circuit and a resistance connected betweensaid battery and said integrated circuit, said resistance having a valuesubstantially larger than the internal resistance of the battery andoperable for producing a voltage drop equal to said battery voltagelevel minus said operating voltage level, and a capacitor of 5 to 10 μfconnected in parallel with the battery and operable for deliveringcurrent peaks to the load.
 13. The apparatus of claim 12 wherein saidvoltage drop is on the order of 1.3 V.
 14. An electronic apparatusadapted to be energized by a long-life lithium-iodine battery having aninternal resistance and a battery voltage level, said apparatusincluding an integrated circuit operable to be powered at an operatingvoltage level lower than battery voltage level, a load controlled bysaid integrated circuit and a resistance connected between said batteryand said integrated circuit, said resistance having a valuesubstantially larger than the internal resistance of the battery andoperable for producing a voltage drop equal to said battery voltagelevel, minus said operating voltage level, and a capacitor of 5 to 10 μfconnected in parallel with the integrated circuit and operable fordelivering current peaks to the load.
 15. The apparatus of claim 14wherein said voltage drop is on the order of 1.3 V.